1. Field of the Invention
The present invention relates to an organic light-emitting apparatus using an organic light-emitting element.
2. Description of the Related Art
As a light-emitting apparatus in which light-emitting elements are disposed in a matrix pattern to constitute a display surface, there is known an organic light-emitting apparatus using an electroluminescent element (organic EL element) having light-emitting layers formed of an organic light-emitting material. In such a light-emitting apparatus, since the elements constituting pixels emit light by themselves, there are advantages that there is no need for provision of a backlight unlike a liquid crystal display, that the response speed is large, and that the viewing angle dependency is small. These advantages make the light-emitting apparatus promising as a flat panel display that succeeds to the liquid crystal display.
A conventional organic EL element has a structure in which a hole injection electrode (anode), an EL light-emitting layer (hereinafter sometimes, referred to as “emission layer”, and an electron injection electrode (cathode) are stacked in the mentioned order. In an organic EL element with such a structure, electrons injected from the cathode into the EL emission layer and holes injected from the anode to the EL emission layer are recombined to generate excitons. The organic EL element emits light by utilizing light emitted when the excitons return to a ground state.
Known light-emitting apparatuses that use organic EL elements include an active matrix type organic light-emitting apparatus. A conventional active matrix type light-emitting apparatus controls the emission luminance through amplitude modulation or time modulation while controlling on/off of light emission by switching with TFTs on and off (see Japanese Patent Application Laid-Open No. H08-054836). In the active matrix light-emitting apparatus, a first electrode on the TFT substrate side is patterned pixel electrodes and a second electrode opposing the substrate is a common electrode. Further, by adopting a top emission structure in which light is extracted from the side opposite to the substrate side, the pixel aperture ratio can be improved and higher luminance and higher definition can be obtained.
In the organic light-emitting apparatus adopting the top emission structure where light is extracted from the side opposite to the substrate side, the first electrode is desirably formed of a highly reflective material and the second electrode needs to be formed of a transparent conductive film. The first electrode is often formed of a conductive film having high reflectance or a stack of a transparent conductive film and a metal conductive film having high reflectance. Indium tin oxide (ITO), for example, is employed as the transparent conductive film. However, most of transparent conductive materials including ITO are low in conductivity and, when used for a common electrode for pixels, cause a voltage drop due to the sheet resistance thereof. As a result, the current that flows in the pixels becomes nonuniform and unevenness of the emission luminance is generated in the display surface.
As a solution to this problem, Japanese Patent Application Laid-Open No. 2001-230086 discloses a method of reducing surface resistance by forming a second electrode of a main electrode and an auxiliary electrode. Japanese Patent Application Laid-Open No. 2004-207217 discloses a solution in which a layer that is identical to a layer constituting a first electrode is disposed between pixels and allowed to function as an auxiliary electrode of a second electrode.
Further, Japanese Patent Application Laid-Open No. 2005-158493 discloses a structure in which a cathode line (conductive portion) is provided between a pixel electrode, which is a substrate side electrode, and a substrate, and a planarizing insulating film is provided between the pixel electrode and the cathode line.
However, in the case where an auxiliary electrode is disposed between pixels as disclosed in Japanese Patent Application Laid-Open Nos. 2001-230086 and 2004-207217, there is a problem that the pixel aperture ratio is reduced.
On the other hand, in the EL apparatus disclosed in Japanese Patent Application Laid-Open No. 2005-158493, the reduction of pixel aperture ratio is suppressed to some degree since the cathode line (conductive portion) is provided below the pixel electrode. However, when the cathode line provided below the pixel electrode has an electric potential different from that of the pixel electrode, a capacitance is generated between the two. The influence of such a capacitance on light emission of an organic light-emitting element is not considered in Japanese Patent Application Laid-Open No. 2005-158493. In particular, the influence of such a capacitance on light emission of organic light-emitting elements of different emission colors that together constitute an organic light-emitting apparatus.
Further, when the conductive layer provided below the pixel electrode is a reflective layer, light emitted from an organic functional layer is reflected by the reflective layer, thereby causing optical interference. However, the influence of optical interference is not considered in Japanese Patent Application Laid-Open No. 2005-158493. In particular, in the case of an organic light-emitting apparatus with organic light-emitting elements of different emission colors, the conditions of optical interference vary depending on the emission color, which has, however, not been considered.